The purpose of this research is to engineer a non-invasive, meso-scale (5 mm) biopsy probe which is capable of 2-photon microscopic imaging. 2-photon microscopic imaging is based on the non-linear excitation of fluorophores using infrared radiation. 2-photon fluorescence microscope has the advantage of 3-D resolution, fluorescence contrast to identify tissue signatures, deep image penetration into highly turbid tissues (200-500 microns), and limited tissue photodamage. 2-photon optical biopsy may be used to complement traditional excisional biopsy in 3 areas: (1) the precise selection of the correct site for excisional biopsy, (2) avoiding missed diagnosis/random sampling, and (3) to ensure complete removal of diseased tissues. Although the utility of macro-scale 2-photon systems in biological studies has been demonstrated in neurobiology and embryology, these systems are only suited for external examination. 1 may find miniaturized 2-photon systems, however these devices rely on short-length optical paths which would prohibit their use in endoscopic examination. Device size, optical path length, and imaging speed are the main barriers to the migration of this technology to endoscope-based diagnosis equipment. The proposed work is unique in that it solves the miniaturization and speed problems via the integration of a micro-optical bench and a multi-axis, high speed MEMS scanning stage. We will build upon this work to (a) engineer a meso-scale device which scans a laser light over a 150x150x150 micronS tissue volume, (b) engineer a micro-optical system which transports the laser energy to and from the sample, (c) integrate the scanning and optical systems into an endoscope probe, and (d) assess the performance of the probe in tissue phantoms. We hope the successful completion of this project will lead to first generation devices that enable evaluation of 2-photon optical biopsy in clinics. A number of preliminary studies have been completed to demonstrate the feasibility of this project: (1) The use of 2-photon to image cellular structures based on autofluorescence, (4) the distribution of tissue biochemical constituents has been resolved based on their 2-photon spectra. (5) the key 2-photon photodamage mechanisms were identified, (5) the engineering challenges associated with delivery of ultra-short light pulses were solved, and (6) the maximum permissible laser power and dosage levels were determined. [unreadable] [unreadable]